Called Sea Star Wasting Disease, it can cause the death of an infected starfish in just a few days. Its effects can be devastating on starfish populations.

The disease has hit before, in southern California in 1983-1984 for example and again in 1997-98. These events were associated with warmer sea temperatures. The current outbreak is more widespread.

It is particularly worrying because one of the starfish affected, Pisaster ochraceus, was the original “keystone species”. This is a species that has a disproportionately large effect on its environment relative to its abundance. Without it the ecosystem would be dramatically different. The concept was first proposed in 1969 using Pisaster ochraceus as a primary example. Within a year of Pisaster ochraceus being removed, biodiversity halved.

Lesions on the animal are the first signs of the disease. Tissue then decays around the lesions which leads to break up of the body and death.